The energy efficiency of light emitting diodes has increased dramatically since they were invented in the 1960s. Many experts in the field compare the continuous improvement of light emitting diodes to Gordon Moore's famous law of microprocessors, with light output per device and energy-efficiency doubling approximately every 18 months. Light emitting diodes can now compete with traditional incandescent and compact fluorescent lighting technologies in terms of light output and energy efficiency.
In one light emitting diode lighting architecture, light emitting diodes of various colors are utilized and the colors of the various diodes are mixed to form a particular color. In one case, there could be red, blue and green light emitting diodes which when turned “on” in particular manners could generate a variety of colors including a white light equivalent.
Each of the light emitting diodes within the lighting architecture could be individually controlled to be “on” for a set period of time within a defined duty cycle using a pulse width modulation technique. In this technique, the intensity of each light emitting diode is defined by the on/off ratio of the diode within the duty cycle, the turning on/off of the diode being a sufficiently short time frame so as not to be perceivable to the human eye. For instance, a duty cycle for the lighting architecture could be set as 1 ms, divided into 256 time segments. In this case, to generate a white light equivalent, the lighting architecture could control the red, blue and green light emitting diodes to be “on” for a relatively similar length of time within each duty cycle. For instance, in one example, the red, blue and green light emitting diodes may each be controlled to be “on” for 128 time segments within the duty cycle (or 50% of the duty cycle). In this case, the intensity of the lighting architecture would be 50% of its potential light output that would occur when all light emitting diodes were “on” 100% of the time.
Light emitting diodes use DC power to generate their light output and therefore lighting architectures employing light emitting diodes require the use of AC to DC converter power supplies if the lighting apparatus is to utilize an AC power source from the public power grid (vs. DC battery power). The cost, lifespan and quality of these power supplies are significant limitations on light emitting diode lighting architectures.
In the sample lighting architecture described above, the power supply will have significantly different current draws when the red, blue and green light emitting diodes are “on” compared to when they are “off”. Significant instantaneous fluctuations in current requirements being placed on the power supply can have a number of negative impacts on the power supply and quality of the light output from the light emitting diodes. For instance, the instantaneous fluctuations in current requirements can result in deteriorating performance of the power supply as significant changes in instantaneous power loads occurring continuously strain the power supply components, such as the voltage stabilizing capacitors. Further, the fluctuations in current requirements can potentially cause the power supply to temporarily not be able to handle a specific current change, and hence potentially cause an undesirable turning “off” of one or more of the light emitting diodes. This may result in a perceivable flicker in the light output or a change in the color of the overall light projected from the lighting architecture. Additionally, when a periodic instantaneous current fluctuation at audio frequencies occurs, an audible ringing or hum may be produced.
Against this background, there is a need for solutions that will better control the light emitting diodes within a lighting apparatus in order to reduce instantaneous current fluctuations within the power supply.